Plastic processing for nicer interiors: how a new process can result in soft-touch instrument panels, a key attribute of today's desirable vehicles.

Blame it on the Germans.

Ever since, certainly, the appearance of the original Audi TT in 1998, automotive journalists everywhere have caused tens--if not hundreds--of thousands of cars not to be purchased because of one thing: the use of hard plastic for the interior trim. For years it had been all about the gaps in sheet metal, which the Japanese vehicle manufacturers had mastered. But with the appearance of the TT and an array of other cars from Audi, BMW, Mercedes, Porsche, and VW, the inside mattered.

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Of course, getting the soft touch that is so endearing to so many is not always particularly simple nor economical. And clearly, those two factors go a long way toward making things happen (or not) in the auto industry today.

One development for accomplishing the goals of soft touch within the simple and economical parameters, which is expected to go into production next year, is called the "Dolphin Process." This process is the result of collaborative work between Engel, an Austrian injection molding machine manufacturer (www.engelglobal.com), material supplier BASF (www.basf.com), material supplier P-Group (www.p-group.biz), and tooling firm Georg Kauffmann Formenbau (www.gktool.ch). Through this collaborative work, the process that combines injection molding and foam molding in one machine has been propelled toward this potential production in a comparatively short amount of time, as it was introduced in 2006.

Typically, creating a soft-touch interior component involves multiple stages, such as creating an instrument panel through sequential injection molding, back foaming, and film lamination. Not only is that method involved, but unless there is a comprehensive lean production system in place, issues of inventory and logistics can add to the cost of the parts produced.

Dolphin is essentially "done-in-one."

First, there is injection molding of a glass-fiber reinforced PBT/ASA (polybutylene terephthalate/acrylic-styrene-acrylonitrile) material to create the body of the panel. Then, there is overmolding with a foam-able thermoplastic polyester. This step involves the use of the MuCell process, a microcellular foaming approach that was originally developed at MIT, and then commercialized by Trexel (www.trexel.com). And there it is, a molded part with a soft touch and a compact skin.

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It should be noted that this isn't something that can be performed in just any injection molding machine, as there is complexity in the process. For Dolphin, the machine technology is an Engel duo dual-platen combi M. In operation, the injection unit for the core, the first operation, is mounted behind the stationary platen. The injection unit for the overmolded foam is mounted on and travels with the rear side of the moving platen in place of the conventional ejector. The plasticizing unit on this platen has necessary equipment for the foaming operation (e.g., nitrogen gas injectors). To move the injection molded component to the overmolding station there is a 180[degrees] rotation of the central block.

The benefits to this approach are several. Among them are the fact that a single machine is required, which has ramifications including reduced floor space and no transport requirements. Because thermoplastic is being used rather than thermoset, there is material recyclability.

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One trend that is picking up momentum in the North American market is the use of composites consisting of a polypropylene (PP) base resin combined with long-glass fibers (LGF). According to Matthew Marks, product market manager with SABIC Innovative Plastics (www.sabic-ip.com), the experience in Europe with the LGF material is greater than it is in the U.S., as evidenced by applications of the LGFPP material on the lift gate of the Ford Kuga crossover and the Citroen Picasso. It's not that North American manufacturers are without experience with the LGFPP material: Delphi (www.delphi.com) is actually producing instrument panels with STAMAX LGFPP ... for the Mercedes M Class.

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According to Marks, the material provides both processing and performance advantages compared with other materials, such as styrene maleic anhydride (SMA) because thinner parts can be produced without sacrificing thickness (which explains why instrument panels are a good application, as they are long and require stiffness). The consequence of thinner parts is not only that there are cycle time reductions on the order of 15%, but with a thickness of 1.8 to 2.0 mm versus anywhere from 2.2 to 4 mm (with the last being for an unfilled material), the mass savings is on the order of two to five pounds.

Another area where there is even greater savings is in front-end modules. While a steel front-end module can weigh from 13 to 15 lb., a LGFPP composite can be used to produce a module weighing five to six pounds.

Marks says that the material can be used in standard injection molding machines, "but care must be taken not to break up the glass fibers or you'll end up with short glass. This means free-flowing orifices, no check rings or things of that nature." He suggests that people looking to mold the material work closely with the tool maker to assure the process.

by Gary S. Vasilash

* EDITORIAL DIRECTOR